108 Mr. Fox’s further Remarks on the Magnetic Forces. 
tan 6! is very great. But this remark is of no value whatever 
in explaining the very singular phenomena which you have 
observed in the extreme case just mentioned ; nor can I ima- 
gine any reason why there should be a deviation, as there 
was in some of your experiments, when the axis lies in the 
plane of incidence, since everything is then alike on both 
sides of this plane. Indeed the whole of this subject, which 
occupies the latter part of your paper of 1819, is very extra- 
ordinary and interesting ; and I was glad to hear that you had 
resumed the investigation of it, and made many experiments 
which have not been published. 
I wish you would publish them. They seem to be of great 
importance in the present state of optical science. 
Tam, dear Sir, ever truly yours, 
Trin, Coll. Dublin, Dec. 22, 1835. J. MacCuiiacuH. 
XX. Some further Remarks on the Magnetic Forces. By 
R. W. Fox.* 
AM glad that Dr. Ritchie has noticed my remarks on the 
laws of the magnetic forces, because I hope that it will be 
the means of exciting more attention to the subject. I can- 
not, however, admit the justness of his conclusion, unless it 
can be shown that the results of my experiments are conform- 
able to the law of the inverse of the squares of the distances 
throughout the whole series of nine or ten removals of the 
magnet, calculating from any assumed points whatever in 
them. Dr. Ritchie has confined his calculations to only two 
or three distances. 
The magnets which I employed were cylinders of three 
inches long and one tenth of an inch in diameter, and at- 
tracted each other with half the force of contact when sepa- 
rated about 7,5 of aninch. From this minute distance to 
that of } and even +} of an inch, the results were nearlyt in 
accordance with the law of the simple inverse ratio of the di- 
stance, calculating from the contiguous surfaces of the mag- 
nets; and when the same bars were made more strongly 
magnetic, their force, at half an inch, much more nearly ap- 
proximated to the simple, than to the duplicate, inverse ratio 
of the distance. 
* Communicated by the Author. 
+ Lhave used this qualifying word, because at very minute distances the 
diminution of the force did not seem to be quite equal to the inverse 
ratio of the distance; whereas it rather exceeded it towards the end of 
the series. At the distance of 3 of an inch, the force, in the case referred 
to, was about +7',5 of that of contact. 
